STOCKTON — Several students at Hong Kingston Elementary School were reported to have experienced lightheadedness and passed out Wednesday afternoon on campus.

Stockton Unified officials confirmed that four students were taken to area hospitals for further tests after the incident occurred near dismissal time at about 1:50 p.m.

The central Stockton school, located off West Benjamin Holt Drive and Alturas Avenue, was placed on a soft lockdown for a brief period to give first responders easy access to the affected students.

All the affected students were reported as stable and none were admitted.

Jasmine Holland, a mother of three children who are all enrolled at Hong Kingston Elementary, learned about what happened after her fifth-grade daughter came home and was visibly upset after seeing one of her friends pass out.

She received a first recorded message from the school at 3:45 p.m. telling parents the school had gone into a lockdown and several students had fallen ill with strange symptoms, Holland said.

By 6 p.m., she received another automated call with news that as many as 10 children had been affected and that the district was working with the health department and law enforcement to investigate the cause.

It was enough to convince Holland to keep her children from attending class Thursday.

“I was very disturbed with what was going on,” she said, adding that she later heard through word-of-mouth from a school employee that the culprit was a gas leak.

A spokesperson for Pacific Gas & Electric Co. told The Record that no gas leaks were found at or near the school.

To ensure that Hong Kingston was indeed safe for both students and employees, the district continues to investigate to determine the cause. The cafeteria, kitchen, campus food and the air were tested on Wednesday and were cleared.

Officials examined and ruled out issues with the heating, ventilation, and air conditioning systems, roof structure, gas pipes, water faucets, and carbon monoxide and toxicology reports results came back negative.

The school was open Thursday and will remain business as usual.

“It’s terrifying, heartbreaking and very disturbing because we don’t know what exactly is going on,” Holland said. “From the food that their eating, or a gas leak, it could’ve been a terrorist attack for all we know. It’s very unsettling.”

Holland was unsure if she would ultimately keep her children home another day.

“I’ll go up there on Friday and speak with someone in the main office to get an answer,” she said. “If the situation is cleared, I'll let them (go). If they’re still unsure, my children will not be there.”

Contact reporter Nicholas Filipas at (209) 546-8257 or nfilipas@recordnet.com. Follow him on Twitter @nicholasfilipas.